Aircraft interior space is made up of various compartments, such as galleys, crew cabins, stowages, closets, lavatories, crew rest quarters, and other facility and storage monuments. These compartments of typically formed by partitions or structural units that separate one compartment from another. To meet airworthiness requirements on commercial passenger-carrying aircraft for the retention of compartments such as galleys attachment or connection devices must be used to secure them to the aircraft's airframe structure. Commonly, these take two forms: type one securing the lower section of the monument to the floor; and type two securing the upper section to the ceiling. Common practice is to manufacture these parts from a combination of aluminum, stainless steel and titanium. These attachments ultimately secure the monuments to the fuselage (or airframe), which may be by means of seat tracks, cross braces, floor beams and other subsidiary parts of the structure.
Floor attachments normally connect to fixed locations, or “hard points,” within the cabin. These fittings do not allow relocation of the monuments to a new location, unless seat track mountings are used that allow either fore and aft movement, or lateral movement, along the track depending upon the orientation of the track. However, a full range of motion is typically unavailable for monument attachments in an aircraft. Floor attachments, or flutter points for low load bearing floor attachments, are typically bonded with glue and/or bolted to the monument as a secondary process, following manufacture of the monument's structural composite panel. Such an assembly typically uses a viscous liquid adhesive, and forms part of the basic monument structure. Due to the fact that only limited projection beyond the outer envelope of the monument is allowed, the floor fittings are commonly offset to the inside of the monument, and mounted on the composite panel's surface or through the panel to a greater or lesser degree, dependent upon design. Where variations exist in the position of the monument, or the position of the hard point attachments or seat tracks, the floor fitting has to be installed in that specific location during manufacture, and relocation or repositioning is limited and every orientation, change in monument location or change in foot print size requires a new location for the floor attachments as part of the structure.
The existing monument attachment design leads to a bias stress loading to one skin of the composite panel, which often fails to optimize the load path into the structure and can lead to a requirement for additional reinforcement in the form of a metallic plate or “doubler” to help spread the stress more effectively throughout the monument and avoid stress concentrations. Unfortunately, this not only adds weight to the aircraft, but is an inefficient means to distribute the load. More recent floor attachment designs have required adjustment in the Z direction as well as the X and Y planes for purposes of alignment during the installation onto the aircraft, which increases the inward projection.
On monuments such as galleys, this has led to a variation in the width of compartments in order that the wheels of the service carts or trolleys avoid contact with the inward projection of the floor fittings. This, in turn, does not allow standardization of cart bay doors, except for the widest possible dimension. This also impacts the efficiency of air circulation around carts in chilled compartments, and produces variations in the widths of standard guide or protection parts such as rub/bump strips in order to compensate for the different offsets.
Additionally, with chilled or refrigerated galleys the presence of a sizable metallic component projecting through the cart bay wall produces significant undesirable cold bridges that can compromise the integrity of the chilled compartment, from a thermal resistance point of view, and the result is a failure to maintain the specified compartment temperature for maintaining perishable food stuffs during normal aircraft operations.
Another common issue with floor attachments, especially in older aircraft, is corrosion of metallic parts due to the galvanic action of dissimilar metals and contact with moisture, cleaning chemicals, spilt beverages such as fruit juices, teas, coffee, soda and alcoholic beverages served routinely during catering service on the aircraft. The environment is conducive to corrosion due to the presence of moisture and the opportunity for beverages to spill during turbulence and the amount of cleaning that occurs in the aircraft between flights.